The present exemplary embodiments relate generally to heating and cooling. They find particular application in conjunction with heating, ventilation, and air conditioning (HVAC) systems, and will be described with particular reference thereto. However, it is to be appreciated that the present exemplary embodiments are also amenable to other like applications.
By way of background, many residential and small commercial forced air HVAC systems employ Permanent Split Capacitor (PSC) motors and/or an Electronically Commutated Motors (ECMs) to drive blowers. These motors generally include selectable speed taps for indoor speed control. Speed is determined by characteristics of the motor and system configuration parameters, such as duct size and installation, dampers and diffusers, HVAC system size, and the like.
Generally, operating modes for HVAC systems, such as heating, cooling, and constant fan operation, require different operating speeds of the motor. Namely, each operating mode generally has an optimum airflow and/or static pressure based on the physics of the heat exchange mechanism. In a heating mode it is based on a heat exchanger, in cooling mode it is based on a cooling coil, and in a fan mode is the slowest speed that achieves good mixing and/or filtering of air and saves energy, since the fan mode serves to even temperatures in a home and push air through filters. Therefore, different taps and speeds are generally used for different operating modes.
The speeds used for different operating modes are normally selected during commissioning of the system by the installer. The installer generally accomplishes this by making electrical connections to a control system, such that the desired tap and speed are energized by the control system for the appropriate mode of operation (e.g., heating). One problem with this arrangement, however, is that once a tap and speed are selected, the installer has no control of the speed.
Limiting the installer's flexibility to set speed reduces or eliminates their ability to solve common system problems that can be corrected through precision airflow adjustment. For example, in the case of heating, the temperature rise of air leaving a heat pump may be less than that leaving a furnace, thereby reducing comfort. This may be addressable by slowing the air down and making it warmer coming out of the vents. As another example, in the case of cooling, an improperly configured HVAC system may lead to low or high humidity levels, thereby reducing comfort.
The flow of air leaving an air conditioner may control humidity levels, where slowing airflow may increase dehumidification. Therefore, if one's house is close to water, the surrounding environment is likely to include high humidity, whereby more dehumidification is desirable. Similarly, if one lives in a dry area, such as Death Valley, the surrounding environment is likely to include low humidity, whereby less dehumidification is preferably.
Fixed speed PSC motors also might cause ductwork and air noise due to the rapid startup of the motor. The rapid start up of the motor will also cause uncomfortable drafts that are lessened using the invention which provides gradual acceleration of the ECM blower motor to reduce the sudden surge of air in the ductwork.
The exemplary embodiment contemplates new and improved systems and/or methods for remedying this and other problems.